Refractory composition

ABSTRACT

A refractory material is premixed with a binder consisting essentially of a mixture of sodium silicate and ammonium pentaborate, to give a refractory composition having a relatively short setting time when mixed with a given amount of water which setting time is predetermined by selecting a weight ratio for the silicate and the pentaborate within a given range.

HID-U40 AU 112 EX Dreyling et al. 1451 Apr. 18, I972 [54] REFRACTORYCOMPOSITION [72] Inventors: Alfred P. Dreyling; Lewis J. Dreyling, both{56] References Cited of East Brunswick, NJ. UNITED STATES p ATENTS I 1Assisnw Q s y p y 2,812,241 11/1957 Austin et al 106/59 {22] Filed, 11969 3,257,217 6/1966 Van Dreser et al ..l06/58 {21] Appl.No.: 862,817Primary Examiner-James E.Poer

. Attorney-Connolly & Hutz Related U.S. Application Data [63]Continuation-impart f Ser. No. 751,506, Aug. 9, [571 ABSTRACT 1968,abandoned, whlch a commuauon'mpan of A refractory material is premixedwith a binder consisting es- 391,182, 21, 1964, abandmedsentially of amixture of sodium silicate and am 'um' entabgrate, to give a refractorymum-5565a relative y {52] US. Cl ..l06/55, 106/57, 106/58, short Settingtime when mixed with a given amount f water 106/591 06/651 106/ 84 whichsetting time is predetermined by selecting a weight ratio [51] Int. Cl...C04b 35/04, C04b 35/42 f the silicate and the pentaborate within agiven Inga [58] Field of Search 106/57, 55, 58, 59, 74, 84, 106/65 2Claims, 2 Drawing Figures REFRACTORY comrosmon SUMMARY OF INVENTION Thisapplication is a continuation-in-part of application Ser. No. 751,506,filed Aug. 9, 1968 by Alfred P. Dreyling and Lewis J. Dreyling forRefractory Composition, now abandoned, and which in turn was acontinuation-in-part of application Ser. No. 391,182, filed on Aug. 21,1964 by Alfred P. Dreyling and Lewis J. Dreyiing for RefractoryCompositions and Method of Controlling Setting Times, now abandoned.

This invention relates to refractory compositions of the type used inrepairing furnaces and more particularly to binders contained thereininitially to set and hold the refractory particles in place until heatis applied to fire the composition to its ultimate refractoriness.

I-leretofore the demand for quick setting refractory compositions hasbeen supplied by the use of quick setting cements, such as calciumaluminates but such cements result in products having a high degree ofshrinkage. Other expedient used as a binding media for refractoryproducts include sodium silicate, borax, etc. But these materialsrequire the evaporation of the water contained in the mass to obtainhardening sufficient to allow heating to higher temperature withoutdifficulties entailed by the presence of water. The use of heat indrying and setting also detracts from the strength of the composition.

According to the present invention, improved refractory compositions areprepared by mixing with refractory material in fine grain form, bindermaterial comprising a plurality of ingredients whose proporation may bevaried within a given range so as to predetermine the setting time ofthe refractory composition when given amounts of water are added toproduce ramming, trowelling or spraying mixtures and this withoutlowering the refractoriness of the composition in any material degree.Or the binder materials may be formulated with added barriers so thatwithout the addition of water they may be stored over quite long periodsof time without change that would affect the refractoriness of thecompositions.

Still further in accordance with the invention, the improved bindermaterials with selected setting times may be used with practically allhigh temperature refractory materials without affecting the performanceof the binding mixtures. Thus, by way of example, refractor rains thatcan be used in refractory compositions with the improved binders includechrome ore, magnesia, zirconia, zircon silicate, zirconium oxide,alumina, mullite, kyanite, and other similar high temperature resistingmaterials or suitable combinations thereof.

The improved binder has less shrinkage upon setting than conventionalbinders of comparable strength.

DRAWINGS FIG. 1 illustrates graphically variations in setting time thatoccur in a binder material consisting essentially of sodium sil-DESCRIPTION As illustrated in the graph FIG. 1 the preferred bindermaterial consists of a mixture of sodium silicate and ammoniumpentaborate in a ratio by weight substantially within the range 0.2 to5.0. These materials after mixture with refractory grains and theaddition of water react to form a hard and tough bond for the refractorygrains and there is a reduction of shrinkage in the end product with noloss of strength.

A suitable sodium silicate for use in practicing the invention isDuponts No. 6 sodium silicate, NaO,:SiO, whose sodium oxide to silicahas a ratio by weight of 1:2. While this sodium silicate is preferredbecause of its ready availability, satisfactory results are obtained forsodium oxide to silicate ratios within the range 12% to 1:4 withoutappreciably affecting the end product.

Sodium silicate reacts with ammonium pentaborate to set a refractorycomposition in a much shorter time than if either of such ingredients isused alone. Furthermore, for any given set of conditions, the timerequired for the binder to set may be varied according to the ratio ofsodium silicate to pentaborate selected but for such set of conditions,the setting time will be the same for any selected ratio.

The binder in the ratio selected is mixed with the refractory materialto formulate the refractory composition. By way of example, therefractory composition may be prepared for use as in the practice of theinvention disclosed in our US. Pat. No. 3,241,987 based upon applicationSer. No. 173,839 filed Feb. 16, 1962 which was copending withapplication Ser. No. 391,182, one of the applications on which thiscontinuationin-part is based. As disclosed in that patent therefractory'portion of the refractory composition may be of the order ofpercent to 98 percent and the binder portion thereof of the order of 2.0percent to 15 percent, such percentages being by weight.

The amount of water added to the dry composition of refractory andbinder in readying it for use will depend upon its type of use, i.e.,whether it is to be rammed, trowelled, or sprayed. Such methods ofapplication are conventional with the amount of water necessary to makea mixture of the proper consistency well within the knowledge of aperson with the ordinary skill of the art.

The graph of FIG. 1 is not intended to show the actual setting time ofall refractory compositions containing a binder of sodium silicate andammonium pentaborate in a given ratio but merely that the setting timeof a mixture of the two in water is much less than the setting time ofeither binder used alone. It is intended to show also that there is adifferent setting tine for different ratios of sodium silicate toammonium pentaborate but that there is a given setting time for eachratio, the conditions otherwise being the same.

- The setting time of a refractory composition having a binderconsisting of sodium silicate with ammonium pentaborate of differentratios will be different for the different ratios and will be differentalso from the corresponding ratios of sodium silicate with ammoniumpentaborate without refractory as shown in FIG. 1. By way of example,and as shown in FIG. 2, if

No. 6 sodium silicate and ammonium entaborate in ratio by weight of l isused as a Binder mixture in a magnesia composition prepared as atrowelling mix containing water to the extent of 10 percent by weight,setting to a rigid strong mass will be accomplished in from 40 to 50minutes. If either of these binders are used alone in the preparation ofthe same type of magnesia composition, setting to a rigid and strongmass would not be accomplished until 12 or more hours had passed. Whenthe weight ratio of sodium silicate to ammonium pentaborate in themagnesia refractory mixture becomes 1.25 the setting time becomes 65 to75 minutes. When the weight ratio of sodium silicate to ammoniumpentaborate becomes 0.4 the setting time becomes 20 to 30 minutes. Thusit can be said that the setting times of refractory compositions ofselected grain sizes may be varied widely within a chosen time bracketby using a ratio of sodium silicate to pentaborate less than infinity,the condition that obtains with an absence of pentaborate and with onlythe silicate present to give a setting time undesirably high, butgreater than zero, the condition that obtains with an absence of sodiumsilicate and with only the pentaborate present which likewise gives asetting time undesirably high. Between these two extremes, there is awide range of ratios by weight of sodium silicate to ammoniumpentaborate in which the setting times will be quite fast. For practicalpurposes this range of ratios by weight of sodium silicate to theammonium pentaborate is substantially from 0.2 to 5.0.

it will be understood that an adjustment in the sodium silicate toammonium pentaborate binder ratio may be made to compensate fordifferent refractory materials, the grain sizes used and the temperatureconditions employed during use in arriving at the desired setting time.The amount of water necessary to activate the binder also has an effectupon the setting time of the refractory composition. Hence, the amountof water added to the composition should be the minimum required forhandling and placing the composition in its selected method of use,i.e., ramming, trowelling, or spraying.

Examples of compositions prepared in accordance with the invention areas follows all percentages being by weight:

EXAMPLE NO. 1

Type T60 Tabular Refractory Alumina (on 6 mesh) 45.0%

materials Type T60 Tabular Alumina (on 60 mesh) 37.0% Alumina A3(powdered) l4.0%

Binder Mixture No. 6 sodium silicate 1.5% Ratio 0.6 Ammonium pentaborate2.5% Total 100.0%

This composition was prepared in a 50 lb. block using 13 lbs. of waterper 100 lbs. of dry material to provide a suitable mix. for trowelling.After mixing and filling the mold, the setting time necessary for aself-supporting block required 3% hours. A similar block containingeither the No. 6 sodium silicate or the ammonium pentaborate in the sameoverall binder percentage required l2 to 14 hours to set to aself-supporting block. It should be noted that the total binderpercentage in this example is only 4 percent and this amount wassufficient to cause the composition to form a tough mass after dryingand firing to 2,950 F. The fired block showed no slump whatsoever afterfiring to 2,950 F. and in addition had less than 1 percent shrinkage.

EXAMPLE NO. 2

Magnesia (thru Refractory mesh on mesh) 50% Materials Magnesia (on 16mesh) l2l Magnesia (powdered) 33.8% Binder Mix- No. 6 sodium silicateL6;

ture Ratio 0667 Ammonium pentaborate 2.4% Wetting Agent Vinsol 0.2%Total l00.01

This composition represents high refractory grains bound together with asilicate to borate ratio in the binder mixture of 0.667 which caused thesetting of a block (self-supporting) of 50 lbs. size as in Example No. 1from a trowelling mix in 3 hours. When fired to 2,950 F., this blockshowed no shrinkage whatsoever.

Applicants are aware that proposal has been made to produce a refractorybinder by mixing a refractory material with sodium silicate and analkali metal or alkali earth metal salt of boric acid to prevent lumpingor setting under storage and shipping conditions and that for suchbinder mixtures claim has been made of improved crushing strengths afterheating to temperatures at least of the order C. the alkali metal andthe alkali earth metal salts of boric acid that have been proposed arequite stable and any reaction they promote toward enhancing a bindingeffect depends upon their reaching temperatures of the order of theirboiling points. For the most part such temperatures are quite high.

Ammonium pentaborate on the other hand is not stable in the presence ofsodium silicate and water. It starts to decompose even at roomtemperature. The volatile Nl-l, radical is driven off forming transientor nascent boric acid which reacts with the sodium silicate to effectits solidificatio e surface of the refracigry ma t e rtal present, LC.magnesia by way of example. [he coating or bond which is formed on therefractory particles is a hard crystalline sodium-silicate boratecomposition containing water of crystallization. The reaction starts assoon as the sodium silicate, ammonium pentaborate and water are in thepresence of each other. The instant binder mixtures can be varied as totheir setting time control as well as to their suitability for use witha chosen refractory material. They may be employed with any of thecommonly used high temperature refractory materials, either alone or incombinations thereof, and still control the desired setting times and inaddition the shrinkage in the end product.

The instant binder mixtures may be used in the processes disclosed inUS. Pat. Nos. 3,093,496 and 3,093,497 both dated June ll, l963.

The invention is therefore one which may be used in a great number ofrefractory compositions where speed in setting is of the essence inorder to save down time on furnaces. In addition, its low shrinkagefactor precludes early failure of the composition by preventing openingsin which the heat may enter to deteriorate the heat fired refractorymaterial.

The refractory grains should be sized for each end use but this has noeffect on the pre-chosen binder mixtures but it does have an effect onthe shrinkage factor and the ability of the final product to withstandthe effect of heat and flame regardless of shape or size.

We claim:

1. A refractory composition suitable for use as a ramming, trowelling,or spraying mixture and characterized by its ability to react inpredetermined time and in appropriate amount of water to form a hardcrystalline sodium-silicate-borate coating composition on thesurfmamaflmined in the composition to bind such particles togetherpreparatory to firing to ultimate refractoriness, said refractorycomposition comprising refractory material in selected grain sizes and,based on the weight of the refractory composition, from 2 percent to l5percent of binder consisting essentially of sodium silicate and ammoniumpentaborate present in a ratio of sodium silicate to ammoniumpentaborate substantially within the range of0.2 to 5.0:1.

2. A refractory composition according to claim 1, wherein the sodiumoxide to silica ratio in the sodium silicate is within the range 12 /2to 1:4.

2. A refractory composition according to claim 1, wherein the sodiumoxide to silica ratio in the sodium silicate is within the range 1: 1/2to 1:4.